Add decrypt, refactor

backend/interface.go

@@ -0,0 +1,21 @@
+package backend
+
+type Type string
+
+const (
+	Blob     Type = "blob"
+	Key           = "key"
+	Lock          = "lock"
+	Snapshot      = "snapshot"
+	Tree          = "tree"
+)
+
+type Server interface {
+	Create(Type, []byte) (ID, error)
+	Get(Type, ID) ([]byte, error)
+	List(Type) (IDs, error)
+	Test(Type, ID) (bool, error)
+	Remove(Type, ID) error
+
+	Location() string
+}